Exhibit 99.4

                        REGISTRATION RIGHTS AGREEMENT




                        Dated as of September 22, 1997

 
 

            REGISTRATION RIGHTS AGREEMENT, dated as of September 22, 1997,
by and between McKesson Corporation (the "Company"), and 399 Venture Partners,
Inc. ("399 Venture").

      1. Introduction; Term of Agreement. The Company is a party to the
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separate Agreement and Plan of Merger (the "Merger Agreement"), dated as of
September 22, 1997, among the Company, Patriot Acquisition Corp. and AmeriSource
Health Corporation, a Delaware Corporation ("AmeriSource"), pursuant to which
the Company and AmeriSource have agreed, that a wholly owned subsidiary of the
Company, Patriot Acquisition Corp., shall be merged with and into AmeriSource
with AmeriSource as the surviving corporation, and shareholders of AmeriSource
to be entitled to shares of common stock of the Company (the "Common Stock") in
respect of their shares of AmeriSource as specified in the Merger Agreement.
This Agreement shall become effective upon the Effective Time (as defined in the
Merger Agreement). This Agreement shall terminate and be of no further force and
effect at such time as the holders of Registrable Securities in the aggregate
own less than 25% of the Registrable Securities owned by such holders at the
Effective Time. Certain capitalized terms used in this Agreement are defined in
section 3 hereof; references to sections shall be to sections of this Agreement.

      2. Registration under Securities Act, etc.
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      2.1 Registration on Request.
          -----------------------

            (a) Demand Request. Upon the written request of the
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Initiating Holder, requesting that the Company effect the registration
under the Securities Act of all or part of such Initiating Holder's
Registrable Securities and specifying the intended method or
methods of disposition thereof (a "Demand Request"), the Company will, as
promptly as reasonably practicable but in no event later than 20 days
after such request, give written notice of such requested registration to
all registered holders of Registrable Securities 

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who would be entitled to participate in such registration, and thereupon the
Company will, subject to the terms of this Agreement, use its best efforts to
effect the registration under the Securities Act of:

                  (i) the Registrable Securities which the Company has
      been so requested to register by such Initiating Holder for
      disposition in accordance with the intended method or methods of
      disposition stated in such request;

                  (ii) all other Registrable Securities the holders of
      which shall have made a written request to the Company for
      registration thereof within 30 days after the giving of such
      written notice by the Company (which request shall specify the
      intended method or methods of disposition of such Registrable
      Securities);

                  (iii) all shares of Common Stock which the Company may
      elect to register in connection with the offering of Registrable
      Securities pursuant to this section 2.1; and

                  (iv) all shares of Common Stock which the Company may
      be required to register in connection with "piggyback" or
      incidental registration rights granted to any other Person;

all to the extent requisite to permit the disposition (in accordance with the
intended method or methods of distribution specified in the Demand Request) of
the Registrable Securities and the additional shares of Common Stock, if any, so
to be registered, provided, however, that each such Demand Request shall be for
a number of shares of Common Stock which represent at least 25% of the aggregate
Registrable Securities received by the holders of Registrable Securities as of
the Effective Time (the "Minimum Demand Amount"), unless the Demand Request is
the last Demand Request available hereunder, in which event the Demand Request
may cover the remainder of the Registrable Securities even if such amount of
Registrable Securities is less than the Minimum Demand Amount. Subject to the
provisions of section 2.1(d), the Initiating Holder will have the right pursuant
to this section 2.1(a) to make an aggregate of two Demand Requests.

      Without limiting the generality of the foregoing, the Initiating Holder
shall have the right to request registration pursuant to this section 2.1 and
specify that one of the methods of disposition of Registrable Securities shall
be a block trade or trades involving Registrable Securities held by the
Initiating Holder and that, in connection therewith, the Company shall file with
the Commission
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a registration statement under Rule 415 covering all of the Registrable
Securities to be sold in the block trade or trades. In such case, the Company
shall file an appropriate shelf registration statement with the Commission as
promptly as reasonably practicable and in accordance with the provisions of
section 2.3. Subject to the provisions of section 2.1(d), any shelf registration
which involves a block trade or block trades as an intended method of
disposition, whether or not any such block trade is made, shall be considered as
the exercise of one of the two Demand Requests permitted by this section
2.1(a). Notwithstanding anything herein to the contrary, it is understood and
agreed that the Initiating Holder shall not be entitled to make a Demand Request
for registration pursuant to this section 2.1(a) until the date which is the
sixtieth day after the Effective Time and, in the event the Initiating Holder
makes such a request, the Company shall use its best efforts to file a
registration statement with the Commission with respect to such request not
later than the thirtieth day following such request. It is furthermore
understood and agreed that if the Initiating Holder makes a Demand Request on or
within ten days after such sixtieth day, the provisions of section 2.1(g) shall
not apply and the Company shall not be entitled to initiate a Delay Period as
therein provided, except as required by applicable law arising from events
outside of the control of the Company.

      (b) Registration Statement Form. Registrations under this section
          ---------------------------
2.1 shall be on such appropriate registration form of the Commission (i)
as shall be selected by the Company and, as shall be reasonably
acceptable to the Initiating Holder of the Registrable Securities so to
be registered and (ii) as shall permit the disposition of such
Registrable Securities in accordance with the intended method or methods
of disposition specified in the request for such registration.

      (c) Expenses. The Company will pay all Registration Expenses in
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connection with any registration requested pursuant to this section 2.1
(including any registration deemed not to be "effected" under section
2.1).

      (d) Effective Registration Statement. A registration requested
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pursuant to this section 2.1 shall not be deemed to have been effected (and
therefore not requested for purposes of the limitations in section 2.1(a) on the
number of requests for registration that can be made pursuant to section 2.1(a))
(i) unless a registration statement with respect thereto has become effective
and the holders of Registrable Securities have sold at least 90% of the
Registrable Securities which they have requested the Company to register,
provided that a registration which does not become effective after the Company
has filed a registration statement with respect thereto solely by reason of the
refusal to proceed of the Initiating Holder (other than a refusal to proceed
based upon the advice of counsel relating to a matter with respect to the
Company) shall be deemed to have been effected by the Company at the request of
the Initiating Holder unless the Initiating
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Holder shall have elected to pay all Registration Expenses in connection with
such registration, (ii) if, after it has become effective, such registration
becomes subject to any stop order, injunction or other order or requirement of
the Commission or other governmental agency or court for any reason, or (iii) if
the conditions to closing specified in the purchase agreement or underwriting
agreement entered into in connection with such registration are not satisfied,
other than by reason of some act or omission by the Initiating Holder or any
other holder of Registrable Securities.

      (e) Selection of Underwriters. If a requested registration pursuant
          -------------------------
to this section 2.1 involves an underwritten offering, the underwriter or
underwriters thereof shall be selected by the Initiating Holder from a
list of underwriters to be agreed upon by the Initiating Holder and the
Company.

      (f) Priority in Requested Registrations. If a requested
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registration pursuant to this section 2.1 involves an underwritten offering, and
the managing underwriter shall advise the Company in writing (with a copy to
each holder of Registrable Securities requesting registration) that, in its
opinion, the number of securities requested to be included in such registration
(including securities of the Company which are not Registrable Securities)
exceeds the number which can be sold in such offering within a price range
acceptable to the holders of a majority of the Registrable Securities requested
to be included in such registration, the Company will include in such
registration, to the extent of the number which the Company is so advised can be
sold in such offering, (i) first, Registrable Securities requested to be
included in such registration by any holders of Registrable Securities, pro rata
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among such holders requesting such registration on the basis of the number of
such securities requested to be included by such holders and (ii) second,
subject to section 2.1(a) hereof, securities the Company proposes to sell and
other securities of the Company included in such registration by other holders
who may have "piggyback" or incidental registration rights.

      (g) Delay Periods. The Company shall be entitled to postpone the
          -------------
filing of any registration statement otherwise required to be prepared and filed
by the Company pursuant to this section 2, or suspend the use of any effective
registration statement under this section 2, for a reasonable period of time,
but not in excess of 90 days (a "Delay Period"), if any executive officer of the
Company determines that in such executive
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officer's reasonable good faith judgment the registration and distribution of
the Registrable Securities covered or to be covered by such registration
statement would materially interfere with any pending material financing,
acquisition or corporate reorganization or other material corporate development
involving the Company or any of its subsidiaries or would require premature
disclosure thereof and promptly gives the Initiating Holder written notice of
such determination, and an approximation of the period of the anticipated delay;
provided, however, that (i) the aggregate number of days included in all Delay
Periods during any consecutive 12 months shall not exceed the aggregate of 180
days and (ii) a period of at least 90 days shall elapse between the termination
of any Delay Period and the commencement of the immediately succeeding Delay
Period. Immediately upon receipt of a written notice of suspension, each holder
of Registrable Securities shall cease all disposition efforts with respect to
Registrable Securities held by such holder. If the Company shall so postpone the
filing of a registration statement, the Holders of Registrable Shares to be
registered shall have the right to withdraw the request for registration by
giving written notice within 45 days after receipt of the notice of postponement
or, if earlier, the termination of such Delay Period (and, in the event of such
withdrawal, such request shall not be counted for purposes of determining the
number of Demand Requests for registration to which the Initiating Holder of
Registrable Shares is entitled pursuant to this section 2). The time period for
which the Company is required to maintain the effectiveness of any registration
statement shall be extended by the aggregate number of days of all Delay Periods
during such registration. The Company shall not be entitled to initiate a Delay
Period unless it shall (A) to the extent permitted by agreements with other
security holders of the Company, concurrently prohibit sales by such other
security holders under registration statements covering securities held by such
other security holders and (B) in the case of a delay arising as a result of
premature disclosure, in accordance with the Company's policies from time to
time in effect, forbid purchases and sales in the open market by senior
executives of the Company.

      2.2 Incidental Registration.
          -----------------------

      (a) Right to Include Registrable Securities. If the Company at any
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time proposes to register any of its shares of Common Stock (other than
in connection with a registration of securities which are convertible or
exchangeable into Common Stock) under the Securities Act (other than by a
registration on Form S-4 or S-8, or any successor or similar forms and
other than pursuant to section 2.1), whether or not for sale for its own
account, it will each such time give prompt written notice to all holders
of Registrable Securities of its intention to do so and of such holders'
rights under this section 2.2. Upon the written request of any such
holder made within 30 days after the receipt 

                                       6

 
of any such notice (which request shall specify the Registrable Securities
intended to be disposed of by such holder and the intended method or methods of
disposition thereof), the Company will, subject to the terms of this Agreement,
use its best efforts to effect the registration under the Securities Act of all
Registrable Securities which the Company has been so requested to register by
the holders thereof, to the extent requisite to permit the disposition (in
accordance with the intended method or methods of distribution thereof specified
in the requests of such holders) of the Registrable Securities so to be
registered, by inclusion of such Registrable Securities in the registration
statement which covers the securities which the Company proposes to register;
provided that if, at any time after giving written notice of its intention to
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register any securities and prior to the effective date of the registration
statement filed in connection with such registration, the Company shall
determine for any reason either not to register or to delay registration of such
securities, the Company may, at its election, give written notice of such
determination to each holder of Registrable Securities and, thereupon, (i) in
the case of a determination not to register, shall be relieved of its obligation
to register any Registrable Securities in connection with such registration (but
not from its obligation to pay the Registration Expenses in connection
therewith), without prejudice, however, to the rights of any holder or holders
of Registrable Securities entitled to do so to request that such registration be
effected as a registration under section 2.1, and (ii) in the case of a
determination to delay registering, shall be permitted to delay registering any
Registrable Securities, for the same period as the delay in registering such
other securities. No registration effected under this section 2.2 shall relieve
the Company of its obligation to effect any registration upon request under
section 2.1, nor shall any such registration hereunder be deemed to have been
effected pursuant to section 2.1. The Company will pay all Registration Expenses
in connection with each registration of Registrable Securities requested
pursuant to this section 2.2, and each Requesting Holder whose Registrable
Securities are included in a registration requested pursuant to this section 2.2
will pay any underwriting discounts and commissions and fees of such holder's
counsel in connection therewith.

      (b) Priority in Incidental Registrations. If (i) a registration
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pursuant to this section 2.2 involves an underwritten offering of the
securities so being registered, whether or not for sale for the account
of the Company, to be distributed (on a firm commitment basis) by or
through one or more underwriters of recognized standing under
underwriting terms appropriate for such a transaction, (ii) the
Registrable Securities so requested to be registered for sale for the
account of holders of Registrable Securities are not also to be included
in such underwritten offering (either because the Company has not 

                                       7

 
been requested so to include such Registrable Securities pursuant to section
2.4(b) or, if requested to do so, is not obligated to do so under section
2.4(b)), and (iii) the managing underwriter of such underwritten offering shall
inform the Company and holders of the Registrable Securities requesting such
registration by letter of its belief that the number of securities requested to
be included in such registration exceeds the number which can be sold in (or
during the time of) such offering, then the Company will include in such
registration:

                  (i) first, all the securities the Company proposes to
      sell for its own account,

                  (ii) second all securities of any other holder who has
      made a demand for registration, and

                  (iii) third, to the extent that the number of
      securities which the Company and any such other holders proposed to
      include pursuant to clauses (i) and (ii) is less than the number of
      securities which the Company has been advised can be sold in such
      offering, the number of such Registrable Securities requested to be
      included in such registration by the Requesting Holders pursuant to
      this section 2.2(a) hereof shall be allocated pro rata among all
      such Requesting Holders on the basis of the relative number of
      Registrable Securities each such holder has requested to be
      included in such registration.

      2.3 Registration Procedures. Subject to section 2.1(a), if and
          -----------------------
whenever the Company is required to effect the registration of any
Registrable Securities under the Securities Act as provided in sections
2.1 and 2.2, the Company shall, as expeditiously as reasonably possible:

                  (i) prepare and file with the Commission the requisite
      registration statement to effect such registration (including such
      audited financial statements as may be required by the Securities
      Act or the rules and regulations promulgated thereunder) and
      thereafter cause such registration statement to become and remain
      effective for a period of at least 120 days, provided, however that
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      the Company may discontinue any registration of its securities
      which are not Registrable Securities (and, under the circumstances
      specified in section 2.2(a), its securities which are Registrable
      Securities) at any time prior to the effective date of the
      registration statement relating thereto;

                  (ii) prepare and file with the Commission such
      amendments and supplements to such registration statement and the
      prospectus used in connection therewith as may be necessary to keep
      such registration statement effective for 

                                       8

 
      a period of at least 120 days and to comply with the provisions of the
      Securities Act with respect to the disposition of all securities covered
      by such registration statement until the earlier of such time as all of
      such securities have been disposed of in accordance with the intended
      methods of disposition by the seller or sellers thereof set forth in such
      registration statement or such other time as is required by the Securities
      Act;

                  (iii) permit any holder of Registrable Securities which 
      holder, in its reasonable judgment, might be deemed to be an underwriter
      or a controlling person of the Company, to participate in the preparation
      of such registration or comparable statement and to require the insertion
      therein of material, furnished to the Company in writing, which in the
      reasonable judgment of such holder and its counsel should be included;

                  (iv) furnish to each seller of Registrable Securities
      covered by such registration statement and each Requesting Holder
      and each underwriter, if any, of the securities being sold by such
      seller such number of conformed copies of such registration
      statement and of each such amendment and supplement thereto (in
      each case including all exhibits), such number of copies of the
      prospectus contained in such registration statement (including each
      preliminary prospectus and any summary prospectus) and any other
      prospectus filed pursuant to Rule 424 under the Securities Act, in
      conformity with the requirements of the Securities Act, and such
      other documents, as such seller and underwriter, if any, may
      reasonably request;

                  (v) use its best efforts to register or qualify all
      Registrable Securities and other securities covered by such
      registration statement under such other state securities laws or
      blue sky laws of such jurisdictions as any seller thereof and any
      underwriter of the securities being sold by such seller and any
      Requesting Holder shall reasonably request, to keep such
      registrations or qualifications in effect for so long as such
      registration statement remains in effect, and take any other action
      which may be reasonably necessary or advisable to enable such
      seller and underwriter to consummate the disposition in such
      jurisdictions of the securities owned by such seller, except that
      the Company shall not for any such purpose be required to qualify
      generally to do business as a foreign corporation in any
      jurisdiction wherein it would not but for the requirements of this
      subsection (v) be obligated to be so qualified or to consent to
      general service of process in any such jurisdiction;

                  (vi) furnish to each seller of Registrable Securities
      and each Requesting Holder a signed counterpart, addressed to such
      seller, such Requesting Holder and the underwriters, if any, of:

                           (X) an opinion of counsel for the Company
                  (which shall be outside counsel if outside counsel is
                  rendering such opinion in the transaction and otherwise
                  may be the Company's inside counsel), 

                                       9

 
                  dated the effective date of such registration statement (or,
                  if such registration includes an underwritten public offering,
                  an opinion dated the date of the closing under the
                  underwriting agreement), customary for a transaction of such
                  type, and

                           (Y) a "comfort" letter (or, in the case of any
                  such Person which does not satisfy the conditions for
                  receipt of a "comfort" letter specified in Statement on
                  Auditing Standards No. 72, an "agreed upon procedures"
                  letter), dated the effective date of such registration
                  statement (and, if such registration includes an
                  underwritten public offering, a letter of like kind
                  dated the date of the closing under the underwriting
                  agreement), signed by the independent public
                  accountants who have certified the Company's financial
                  statements included in such registration statement,

      covering substantially the same matters with respect to such
      registration statement (and the prospectus included therein) and,
      in the case of the accountants' letter, with respect to events
      subsequent to the date of such financial statements, as are
      customarily covered in opinions of issuer's counsel and in
      accountants' letters delivered to the underwriters in underwritten
      public offerings of securities (with, in the case of an "agreed
      upon procedure" letter, such modifications or deletions as may be
      required under Statement on Auditing Standards No. 35) and, in the
      case of the accountants' letter, such other financial matters
      customarily covered in a transaction of such type;

                  (vii) notify the holders of Registrable Securities and
      the managing underwriter or underwriters, if any, promptly:

                           (V) when the registration statement, the
                  prospectus or any prospectus supplement related thereto
                  or post-effective amendment to the registration
                  statement has been filed, and, with respect to the
                  registration statement or any post-effective amendment
                  thereto, when the same has become effective:

                           (W) of any request by the Commission for
                  amendments or supplements to the registration statement
                  or the prospectus or for additional information;

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                           (X) of the issuance by the Commission of any
                  stop order suspending the effectiveness of the
                  registration statement or the initiation of any
                  proceedings by any Person for that purpose;

                           (Y) if at any time the representations and
                  warranties of the Company made as contemplated by
                  section 2.4 below cease to be true and correct; and

                           (Z) of the receipt by the Company of any
                  notification with respect to the suspension of the
                  qualification of any Registrable Securities for sale
                  under the securities or blue sky laws of any
                  jurisdiction or the initiation or threat of any
                  proceeding for such purpose;

                  (viii) notify each seller of Registrable Securities
      covered by such registration statement and each Requesting Holder,
      at any time when a prospectus relating thereto is required to be
      delivered under the Securities Act, upon the Company's discovery
      that, or upon the happening of any event as a result of which, the
      prospectus included in such registration statement, as then in
      effect, includes an untrue statement of a material fact or omits to
      state any material fact required to be stated therein or necessary
      to make the statements therein not misleading in the light of the
      circumstances under which they were made, and at the request of any
      such seller or Requesting Holder promptly prepare and furnish to
      such seller or Requesting Holder and each underwriter, if any, a
      reasonable number of copies of a supplement to or an amendment of
      such prospectus as may be necessary so that, as thereafter
      delivered to the purchasers of such securities, such prospectus
      shall not include an untrue statement of a material fact or omit to
      state a material fact required to be stated therein or necessary to
      make the statements therein not misleading in the light of the
      circumstances under which they were made;

                  (ix) make every reasonable effort to obtain the
      withdrawal of any order suspending the effectiveness of the
      registration statement at the earliest possible moment;

                  (x) otherwise use its best efforts to comply with all
      applicable rules and regulations of the Commission, and, if
      required, make available to its security holders, as soon as
      reasonably practicable, an earnings statement covering the period
      of at least twelve months, but not more than eighteen months,
      beginning with the first day of the Company's first full calendar
      quarter after the effective date of such registration statement,
      which earnings statement shall satisfy the provisions of Section
      11(a) of 

                                       11

 
      the Securities Act and Rule 158 thereunder, and will use its best efforts
      to furnish to each such seller and each Requesting Holder at least one
      business day prior to the filing thereof a copy of any amendment or
      supplement to such registration statement or prospectus and shall not file
      any thereof to which any such seller or any Requesting Holder shall have
      reasonably objected on the grounds that such amendment or supplement does
      not comply in all material respects with the requirements of the
      Securities Act or of the rules or regulations thereunder;

                  (xi) provide and cause to be maintained a transfer agent
      and registrar for all Registrable Securities covered by such
      registration statement from and after a date not later than the
      effective date of such registration statement; and

                  (xii) use its best efforts to list all Registrable
      Securities covered by such registration statement on any securities
      exchange on which any of the securities of the same class as the
      Registrable Securities are then listed.

      The Company will not file any registration statement or amendment
thereto or any prospectus or any supplement thereto to which the holders
of at least a majority of the Registrable Securities covered by such
registration statement or the underwriter or underwriters, if any, shall
reasonably object.

      The Company may require each seller of Registrable Securities as to
which any registration is being effected to furnish the Company such
information regarding such seller and the distribution of such securities
as the Company may from time to time reasonably request in writing.

      Each holder of Registrable Securities agrees by acquisition of such
Registrable Securities that, upon receipt of any notice from the Company
of the occurrence of any event of the kind described in paragraph (ix)
of this section 2.3, such holder will forthwith discontinue such holder's
disposition of Registrable Securities pursuant to the registration
statement relating to such Registrable Securities until such holder's
receipt of the copies of the supplemented or amended prospectus
contemplated by paragraph (ix) of this section 2.3 and, if so directed
by the Company, will deliver to the Company (at the Company's expense)
all copies, other than permanent file copies, then in such holder's
possession of the prospectus relating to such Registrable Securities
current at the time of receipt of such notice. In the event the Company
shall give any such notice, the period mentioned in paragraph (ii) of
this section 2.3 shall be extended by the length of the period from and
including the date when each seller of any Registrable Securities 

                                       12

 
covered by such registration statement shall have received such notice to the
date on which each such seller has received the copies of the supplemented or
amended prospectus contemplated by paragraph (ix) of this section 2.3.

      If any such registration statement refers to any holder of
Registrable Securities by name or otherwise as the holder of any
securities of the Company, then such holder shall have the right to
require (i) the insertion therein of language, in form and substance
satisfactory to such holder, to the effect that the holding by such
holder of such securities does not necessarily make such holder a
"controlling person" of the Company within the meaning of the Securities
Act and is not to be construed as a recommendation by such holder of the
investment quality of the Company's securities covered thereby and that
such holding does not imply that such holder will assist in meeting any
future financial requirements of the Company, or (ii) in the event that
such reference to such holder by name or otherwise is not required by the
Securities Act or any similar federal statute then in force, the deletion
of the reference to such holder.

      2.4 Underwritten Offerings:
          ----------------------

      (a) Requested Underwritten Offerings. If requested by the
          --------------------------------
underwriters for any underwritten offering by holders of Registrable
Securities pursuant to a registration requested under section 2.1, the
Company will enter into an underwriting or similar agreement with such
underwriters for such offering, such agreement to be reasonably
satisfactory in substance and form to the Company, each such holder and
the underwriters, and to contain such representations and warranties by
the Company and such other terms as are generally prevailing in
agreements of this type, including, without limitation, indemnities to
the effect and to the extent provided in section 2.7. The holders of the
Registrable Securities will cooperate with the Company in the negotiation
of the underwriting or similar agreement and will give consideration to
the reasonable suggestions of the Company regarding the form thereof,
provided that nothing herein contained shall diminish the foregoing
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obligations of the Company. The holders of Registrable Securities to be
distributed by such underwriters shall be parties to such underwriting
agreement and may, at their option, require that any or all of the
representations and warranties by, and the other agreements on the part
of, the Company to and for the benefit of such underwriters shall also be
made to and for the benefit of such holders of Registrable Securities and
that any or all of the conditions precedent to the obligations of such
underwriters under such underwriting agreement be conditions precedent to
the obligations of such holders of Registrable Securities. No
underwriting or similar agreement shall require any holder of Registrable
Securities to make any representations or warranties to or agreements
with the Company or the underwriters other than 

                                       13

 
representations and warranties or agreements regarding such holder, such
holder's Registrable Securities and such holder's intended method or methods of
distribution and any other representation required by law or to make any
agreements with the Company or the underwriters with respect to indemnification
of any Person or the contribution obligations of any Person that would impose
any obligation which is broader than the indemnity furnished by such holder
pursuant to the provisions of section 2.7. In addition, the Requesting Holders
shall cooperate with the Company in an effort to provide that any such agreement
will contain a provision modifying the indemnification of the underwriter to the
effect that the Company will not be liable to any Person who participates as an
underwriter in the offering or sale of Registrable Securities with respect to
any preliminary prospectus, to the extent that any such loss, claim, damage or
liability of such underwriter results from such underwriter having sold
Registrable Securities to a person to whom there was not sent or given, at or
prior to the written confirmation of such sale, a copy of the final prospectus,
if the Company has previously furnished thereof to such underwriter and such
final prospectus as then amended or supplemented, has corrected any such
misstatement or omission.

      (b) Incidental Underwritten Offerings. If the Company at any time
          ---------------------------------
proposes to register any of its securities under the Securities Act as
contemplated by section 2.2 and such securities are to be distributed by
or through one or more underwriters, the Company will, if requested by
any holder of Registrable Securities as provided in section 2.2 and
subject to the provisions of section 2.2(b), use its best efforts to
arrange for such underwriters to include all the Registrable Securities
to be offered and sold by such holder among the securities to be
distributed by such underwriters. The holders of Registrable Securities
to be distributed by such underwriters shall be parties to the
underwriting agreement between the Company and such underwriters and may,
at their option, require that any or all of the representations and
warranties by, and the other agreements on the part of, the Company to
and for the benefit of such underwriters shall also be made to and for
the benefit of such holders of Registrable Securities and that any or all
of the conditions precedent to the obligations of such underwriters under
such underwriting agreement be conditions precedent to the obligations of
such holders of Registrable Securities. Any such holder of Registrable
Securities shall not be required to make any representations or
warranties to or agreements with the Company or the underwriters other
than representations, warranties or agreements regarding such holder,
such holder's Registrable Securities and such holder's intended method of
distribution and any other representation required by law or to make any
agreements with the Company or the underwriters with respect to
indemnification of any Person or the contribution obligations of any
Person that would impose any obligation which 

                                       14

 
is broader than the indemnity furnished by such holder pursuant to the
provisions of section 2.7. In addition, the Requesting Holders shall cooperate
with the Company in an effort to provide that any such agreement will contain a
provision modifying the indemnification of the underwriter to the effect that
the Company will not be liable to any Person who participates as an underwriter
in the offering or sale of Registrable Securities with respect to any
preliminary prospectus, to the extent that any such loss, claim, damage or
liability of such underwriter results from such underwriter having sold
Registrable Securities to a person to whom there was not sent or given, at or
prior to the written confirmation of such sale, a copy of the final prospectus,
if the Company has previously furnished thereof to such underwriter and such
final prospectus as then amended or supplemented, has corrected any such
misstatement or omission.

      (c) Holdback Agreements.
          -------------------

                  (i) Each holder of Registrable Securities agrees by
      acquisition of such Registrable Securities, if and to the extent so
      required by the managing underwriter, not to sell, make any short
      sale of, loan, grant any option for the purchase of, effect any
      public sale or distribution of or otherwise dispose of any
      securities of the Company, during the 7 days prior to and the 90
      days after any underwritten registration pursuant to section 2.1 or
      2.2 has become effective, except as part of such underwritten
      registration, whether or not such holder participates in such
      registration, provided that the foregoing restrictions shall not
                    --------
      apply with regard to the transfer by the Holders of Registrable Securities
      to any Affiliate or to any other transferee in a private transaction not
      requiring registration under the Securities Act, or to any bona fide
      pledge of such Registrable Securities, provided that such Affiliate or
      other transferee and/or lender or creditor acknowledges in writing that it
      is bound by the provisions of this section 2.4(c). Each holder of
      Registrable Securities agrees that the Company may instruct its transfer
      agent to place stop transfer notations in its records to enforce this
      section 2.4(c).

                  (ii) The Company agrees (X) if so required by the
      managing underwriter not to sell, make any short sale of, loan,
      grant any option for the purchase of, effect any public sale or
      distribution of or otherwise dispose of its equity securities or
      securities convertible into or exchangeable or exercisable for any
      of such securities during the seven days prior to and the 90 days
      after any underwritten registration pursuant to section 2.1 or 2.2
      has become effective, except as part of such underwritten
      registration and except pursuant to registrations on Form S-

                                       15

 
      4, S-8, or any successor or similar forms thereto, and (Y) to cause each
      holder of its securities purchased from the Company at any time after the
      date of this Agreement (other than in a public offering) to agree not to
      sell, make any short sale of, loan, grant any option for the purchase of,
      effect any public sale or distribution of or otherwise dispose of such
      securities during such periods.

      (d) Participation in Underwritten Offerings. No Person may
          ---------------------------------------
participate in any underwritten offering hereunder unless such Person (i)
agrees to sell such Person's securities on the basis provided in any
underwriting arrangements approved, subject to the terms and conditions
hereof, by the Company and the holders of a majority of Registrable
Securities to be included in such underwritten offering and (ii)
completes and executes all questionnaires, indemnities, underwriting
agreements and other documents (other than powers of attorney) required
under the terms of such underwriting arrangements. Notwithstanding the
foregoing, no underwriting agreement (or other agreement in connection
with such offering) shall require any holder of Registrable Securities to
make any representations or warranties to or agreements with the Company
or the underwriters other than representations and warranties regarding
such holder, such holder's Registrable Securities and such holder's
intended method or methods of distribution and any other representation
required by law or to make any agreements with the Company or the
underwriters with respect to indemnification of any Person or the
contribution obligations of any Person that would impose any obligation
which is broader than the indemnity furnished by such holder pursuant to
the provisions of section 2.7.

      2.5 Preparation: Reasonable Investigation. In connection with the
          -------------------------------------
preparation and filing of each registration statement under the
Securities Act pursuant to this Agreement, the Company will give the
holders of Registrable Securities registered under such registration
statement, their underwriters, if any, each Requesting Holder and their
respective counsel and accountants, the opportunity to participate in the
preparation of such registration statement, each prospectus included
therein or filed with the Commission, and each amendment thereof or
supplement thereto, and will give each of them such reasonable access
during normal business hours to its books and records and such
opportunities to discuss the business of the Company with its officers
and the independent public accountants who have certified its financial
statements as shall be necessary, in the opinion of such holders' and
such underwriters' respective counsel, to conduct a reasonable
investigation within the meaning of the Securities Act.

      2.6 Rights of Requesting Holders. The Company will not file any
          ----------------------------
registration statement relating to Common Stock under 

                                       16

 
the Securities Act (other than by a registration on Form S-4 or Form S-8 or in
connection with a registration of securities which are convertible into or
exchangeable for Common Stock), unless it shall first have given to each holder
of Registrable Securities (who would be entitled to participate in such
registration) at the time outstanding (other than any such Person who acquired
all such securities held by such Person in a public offering registered under
the Securities Act or as the direct or indirect transferee of shares initially
issued in such an offering), at least 30 days prior written notice thereof. Any
such Person who shall so request within 30 days after such notice (a "Requesting
Holder") shall have the rights of a Requesting Holder provided in sections 2.3,
2.5 and 2.7. In addition, if any such registration statement refers to any
Requesting Holder by name or otherwise (other than through a document filed by
or on behalf of any Requesting Holder which is incorporated by reference) as the
holder of any securities of the Company, then such holder shall have the right
to require (a) the insertion therein of language, in form and substance
satisfactory to such holder, to the effect that the holding by such holder of
such securities does not necessarily make such holder a "controlling person" of
the Company within the meaning of the Securities Act and is not to be construed
as a recommendation by such holder of the investment quality of the Company's
debt or equity securities covered thereby and that such holding does not imply
that such holder will assist in meeting any future financial requirements of the
Company, or (b) in the event that such reference to such holder by name or
otherwise is not required by the Securities Act or any rules and regulations
promulgated thereunder, the deletion of the reference to such holder.

      2.7 Indemnification.
          ---------------

      (a) Indemnification by the Company. In the event of any
          ------------------------------
registration of any securities of the Company under the Securities Act,
the Company will, and hereby does agree to, indemnify and hold harmless
(i) in the case of any registration statement filed pursuant to section
2.1 or 2.2, the holder of any Registrable Securities covered by such
registration statement and its partners, if any, its and their respective
directors, officers, partners, agents and Affiliates, each other Person
who participates as an underwriter in the offering or sale of such
securities and each other Person, if any, who controls such holder or any
such underwriter within the meaning of the Securities Act, and (ii) in
the case of any registration statement of the Company, any Requesting
Holder and its partners, if any, its and their respective directors,
officers, partners, agents and Affiliates and each other Person, if any,
who controls such Requesting Holder within the meaning of the Securities
Act, against any losses, claims, damages or liabilities, joint or
several, to which such holder or Requesting Holder or partner thereof or
any such director or officer or partner or agent or 

                                       17

 
Affiliate or underwriter or controlling person may become subject under the
Securities Act or otherwise, insofar as such losses, claims, damages or
liabilities (or actions or proceedings, whether commenced or threatened, in
respect thereof) arise out of or are based upon any untrue statement or alleged
untrue statement of any material fact contained in any registration statement
under which such securities were registered under the Securities Act, any
preliminary prospectus, final prospectus or summary prospectus contained
therein, or any amendment or supplement thereto, or any omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements therein not misleading, and the Company will
reimburse such holder, such Requesting Holder, their respective partners and
each such director, officer, partner, agent, Affiliate, underwriter and
controlling person for any legal or any other expenses reasonably incurred by
them in connection with investigating or defending any such loss, claim,
liability, action or proceeding, provided, that the Company shall not be liable
                                 --------
in any such case to the extent that any such loss, claim, damage, liability (or
action or proceeding in respect thereof) or expense arises out of or is based
upon an untrue statement or alleged untrue statement or omission or alleged
omission made in such registration statement, any such preliminary prospectus,
final prospectus, summary prospectus, amendment or supplement in reliance upon
and in conformity with written information furnished to the Company through an
instrument duly executed by such holder or Requesting Holder, as the case may
be, specifically stating that it is for use in the preparation thereof. Such
indemnity shall remain in full force and effect regardless of any investigation
made by or on behalf of such holder or such Requesting Holder or partner thereof
or any such director, officer, partner, agent, Affiliate, underwriter or
controlling person and shall survive the transfer of such securities by such
holder. The indemnity agreement contained in this section 2.7(a) shall not apply
to amounts paid in settlement of any such loss, claim, damage, liability, action
or proceeding if such settlement is effected without the consent of the Company.

      (b) Indemnification by the Sellers. The Company may require, as a
          ------------------------------
condition to including any Registrable Securities in any registration
statement filed pursuant to section 2.3, that the Company shall have
received an undertaking reasonably satisfactory to it from the
prospective seller of such Registrable Securities, to indemnify severally
and hold harmless (in the same manner and to the same extent as set forth
in subsection (a) of this section 2.7) the Company, each director of the
Company, each officer of the Company and each other person, if any, who
controls the Company within the meaning of the Securities Act, with
respect to any statement or alleged statement in or omission or alleged
omission from such registration statement, any preliminary prospectus,
final 
                                       18

 
prospectus or summary prospectus contained therein, or any amendment or
supplement thereto, if such statement or alleged statement or omission or
alleged omission was made in reliance upon and in conformity with written
information furnished to the Company through an instrument duly executed by such
seller specifically stating that it is for use in the preparation of such
registration statement, preliminary prospectus, final prospectus, summary
prospectus, amendment or supplement. Any such indemnity shall remain in full
force and effect, regardless of any investigation made by or on behalf of the
Company or any such director, officer or controlling person and shall survive
the transfer of such securities by such seller. The indemnity agreement provided
for in this section 2.7(b) shall not apply to amounts paid in settlement of any
such loss, claim, damage, liability, action or proceeding if such settlement is
effected without the consent of such seller (which consent shall not be
unreasonably withheld). The parties hereto hereby acknowledge and agree that,
unless otherwise expressly agreed to in writing by holders of Registrable
Securities to the contrary, for all purposes of this Agreement the only
information furnished or to be furnished to the Company for use in any
registration statement, any preliminary prospectus, final prospectus or summary
prospectus contained therein, or any amendment or supplement thereto are
statements specifically relating to (i) transactions between such holder and its
Affiliates, on the one hand, and the Company, on the other hand, (ii) the
beneficial ownership of shares of Common Stock by such holders and its
Affiliates,(iii) the name and address of such holder and (iv) solely in
offerings that are underwritten offerings, the method or methods of distribution
of such holders. The indemnity provided for under this section 2.7(b) shall be
limited in amount to the net amount of proceeds actually received by such seller
from the sale of Registrable Securities pursuant to such registration statement.

      (c) Notices of Claims, etc. Promptly after receipt by an
          -----------------------
indemnified party of notice of the commencement of any action or
proceeding involving a claim referred to in the preceding subsections of
this section 2.7, such indemnified party will, if a claim in respect
thereof is to be made against an indemnifying party, give written notice
to the latter of the commencement of such action, provided that the
                                                  --------
failure of any indemnified party to give notice as provided herein shall
not relieve the indemnifying party of its obligations under the preceding
subsections of this section 2.7, except to the extent that the
indemnifying party is actually prejudiced by such failure to give notice.
In case any such action is brought against an indemnified party, unless
in such indemnified party's reasonable judgment a conflict of interest
between such indemnified and indemnifying parties may exist in respect of
such claim, the indemnifying party shall be entitled to participate in
and to assume the defense thereof, jointly with any other indemnifying

                                       19

 
party similarly notified, to the extent that the indemnifying party may
wish, with counsel reasonably satisfactory to such indemnified party, and
after notice from the indemnifying party to such indemnified party of its
election so to assume the defense thereof, the indemnifying party shall
not be liable to such indemnified party for any legal or other expenses
subsequently incurred by the latter in connection with the defense
thereof other than reasonable costs of investigation. No indemnifying
party shall, without the consent of the indemnified party, consent to
entry of any judgment or enter into any settlement of any such action
which does not include as an unconditional term thereof the giving by the
claimant or plaintiff to such indemnified party of a release from all
liability, or a covenant not to sue, in respect to such claim or
litigation. No indemnified party shall consent to entry of any judgment
or enter into any settlement of any such action the defense of which has
been assumed by an indemnifying party without the consent of such
indemnifying party.

      (d) Indemnification Payments. The indemnification required by this
          ------------------------
section 2.7 shall be made by periodic payments of the amount thereof
during the course of the investigation or defense, as and when bills are
received or expense, loss, damage or liability is incurred.

      (e) Contribution. If the indemnification provided for in the
          ------------
preceding subsections of this section 2.7 is unavailable to an
indemnified party in respect of any expense, loss, claim, damage or
liability referred to therein, then each indemnifying party, in lieu of
indemnifying such indemnified party, shall contribute to the amount paid
or payable by such indemnified party as a result of such expense, loss,
claim, damage or liability in such proportion as is appropriate to
reflect the relative benefits and the relative fault of the Company on
the one hand and the holder or underwriter, as the case may be, on the
other in connection with the distribution of the Registrable Securities
and the statements or omissions which result in any expense, loss, damage
or liability, as well as any other relevant equitable considerations. The
relative fault of the Company on the one hand and of the holder or
underwriter, as the case may be, on the other shall be determined by
reference to, among other things, whether the untrue or alleged untrue
statement of a material fact or omission to state a material fact relates
to information supplied by the Company, by the holder or by the
underwriter and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such statement or
omission.

      The Company and the holders of Registrable Securities agree that it
would not be just and equitable if contribution pursuant to this
subsection (e) were determined by pro rata allocation (even if the
holders, Requesting Holders and any underwriters 

                                       20

 
were treated as one entity for such purpose) or by any other method of
allocation that does not take account of the equitable considerations referred
to in the immediately preceding paragraph. The amount paid or payable by an
indemnified party as a result of the losses, claims, damages and liabilities
referred to in the immediately preceding paragraph shall be deemed to include,
subject to the limitations set forth in the preceding sentence and subsection
(c) of this section 2.7, any legal or other expenses reasonably incurred by such
indemnified party in connection with investigating or defending any such action
or claim.

      Notwithstanding the provisions of this subsection (e), no holder of
Registrable Securities or underwriter shall be required to contribute any
amount in excess of the amount by which (i) in the case of any such
holder the net proceeds received by such holder from the sale of
Registrable Securities or (ii) in the case of an underwriter, the total
price at which the Registrable Securities purchased by it and distributed
to the public were offered to the public exceeds, in any such case, the
amount of any damages that such holder or underwriter has otherwise been
required to pay by reason of such untrue or alleged untrue statement or
omission. No Person guilty of fraudulent misrepresentation (within the
meaning of Section 11(f) of the Securities Act) shall be entitled to
contribution from any person who was not guilty of such fraudulent
misrepresentation. No party shall be liable for contribution under this
section 2.7 except to the extent and under such circumstances as such
party would have been liable to indemnify under this section 2.7 if such
indemnification were enforceable under applicable law.

      3. Definitions. As used herein, unless the context otherwise
         -----------
requires, the following terms have the following respective meanings.

      Affiliate: As defined in Rule 12b-2 promulgated under the Exchange Act.
      ---------

      Beneficially Own or Beneficial Ownership: With respect to any
      ----------------    --------------------
      securities shall mean having "beneficial ownership" of such
      securities (as determined pursuant to rule 13d-3 under the Exchange
      Act), including pursuant to any agreement, arrangement or
      understanding, whether or not in writing. Without duplicative
      counting of the same securities by the same holder, securities
      Beneficially Owned by a person shall include securities
      Beneficially Owned by all Affiliates of such Person and all other
      Persons with whom such person would constitute a "group" within the
      meaning of Section 13 (d) of the Exchange Act and the rules
      promulgated thereunder.

                                       21

 
      Commission: The Securities and Exchange Commission or any other
      ----------
      Federal agency at the time administering the Securities Act.

      Common Stock: As defined in section 1.
      ------------

      Company: As defined in the introductory paragraph of this Agreement.
      -------

      Delay Period: As defined in section 2.1(g).
      ------------

      Demand Request:  As defined in section 2.1(a).
      -------------- 

      Effective Time: As defined in the Merger Agreement.
      --------------

      Exchange Act: The Securities Exchange Act of 1934, or any similar
      ------------
      Federal Statute, and the rules and regulations of the Commission
      thereunder, all as the same shall be in effect at the time.
      Reference to a particular section of the Securities Exchange Act of
      1934 shall include a reference to the comparable Section, if any,
      of any such similar federal statute.

      Initiating Holder: Holders of at least 50% of the Registrable Securities.
      -----------------
      
      Merger Agreement: As defined in section 1.
      ----------------

      Person: A corporation, an association, a partnership, an
      ------
      organization, business, an individual, a governmental or political
      subdivision thereof or a governmental agency.

      Registrable Securities: The Common Stock issued pursuant to the
      ----------------------
      transactions contemplated by the Merger Agreement and any
      securities issued or issuable with respect to any Common Stock by
      way of stock dividend or stock split or in connection with a
      combination of shares, recapitalization, merger, consolidation or
      other reorganization or otherwise. As to any particular Registrable
      Securities, once issued, such securities shall cease to be
      Registrable Securities when (a) a registration statement with
      respect to the sale of such securities shall have become effective
      under the 

                                       22

 
      Securities Act and such securities have been disposed of in accordance
      with such registration statement, (b) they shall have been distributed to
      the public pursuant to Rule 144 (or any successor provision) under the
      Securities Act, (c) they shall have ceased to be outstanding.

      Registration Expenses: All expenses incident to the Company's
      ---------------------
      performance of or compliance with section 2, including, without
      limitation, all registration, filing and NASD fees, all stock
      exchange listing fees, all fees and expenses of complying with
      securities or blue sky laws, all word processing, duplicating and
      printing expenses, messenger and delivery expenses, the fees and
      disbursements of counsel for the Company and of its independent
      public accountants, including the expenses of any special audits or
      "cold comfort" letters required by or incident to such performance
      and compliance, and any fees and disbursements of underwriters
      customarily paid by issuers or sellers or securities, but excluding
      underwriting discounts and commissions and transfer taxes, if any.

      Requesting Holder: As defined in section 2.6.
      -----------------

      Securities Act: The Securities Act of 1933, or any similar Federal
      --------------
      statute, and the rules and regulations of the Commission
      thereunder, all as of the same shall be in effect at the time.
      References to a particular section of the Securities Act of 1933
      shall include a reference to the comparable Section, if any, of any
      such similar Federal Statute.

      4. Rule 144. The Company shall timely file the reports required to
         --------
be filed by it under the Securities Act and the Exchange Act (including
but not limited to the reports under sections 13 and 15(d) of the
Exchange Act referred to in subparagraph (c) of Rule 144 adopted by the
Commission under the Securities Act) and the rules and regulations
adopted by the Commission thereunder and will take such further action as
any holder of Registrable Securities may reasonably request, all to the
extent required from time to time to enable such holder to sell
Registrable Securities without registration under the 

                                       23

 
Securities Act within the limitation of the exemptions provided by (a) Rule 144
under the Securities Act, as such Rule may be amended from time to time, or (b)
any similar rule or regulation hereafter adopted by the Commission. Upon the
request of any holder of Registrable Securities, the Company will (a) deliver to
such holder a written statement as to whether it has complied with the
requirements of this section 4 or (b) take such action as is necessary to allow
transfer of such Registrable Securities in accordance with the provisions of
Rule 144(k) (or any successor provision) under the Securities Act including
without limitation, if necessary, the issuance of new certificates for such
Registrable Securities bearing a legend restricting further transfer.

      5. Amendments and Waivers. This Agreement may be amended and the
         ----------------------
Company may take any action herein prohibited, or omit to perform any act herein
required to be performed by it, only if the Company shall have obtained the
written consent to such amendment, action or omission to act, of the holder or
holders of more than 50% of the shares of Registrable Securities and in the case
of any such amendment, action or omission to act in respect of the first
sentence of Section 4, the written consent of each holder affected thereby. Each
holder of any Registrable Securities at the time or thereafter outstanding shall
be bound by any consent authorized by this section 5, whether or not such
Registrable Securities shall have been marked to indicate such consent.

      6. No Inconsistent Agreements. The Company will not enter into any 
         --------------------------  
agreement which is inconsistent with or violates the rights granted to the 
holders of Registrable Securities in this Agreement.

      7. Nominees for Beneficial Owners. In the event that any
         ------------------------------
Registrable Securities are held by a nominee for the beneficial owner
thereof, the beneficial owner thereof may, at its election, be treated as
the holder of such Registrable Securities for purposes of any request or
other action by any holder or holders of Registrable Securities pursuant
to this Agreement or any determination of any number or percentage of
shares of Registrable Securities held by any holder or holders of
Registrable Securities contemplated by this Agreement. If the beneficial
owner of any Registrable Securities so elects, the Company may require
assurances reasonably satisfactory to it of such owner's beneficial
ownership of such Registrable Securities.

      8. Notices. Except as otherwise provided in this Agreement, all
         -------
notices, requests and other communications to any Person provided for hereunder
shall be in writing and shall be given to such Person (a) in the case of the
Initiating Holder, addressed to 399 Venture Partners, Inc., 399 Park Avenue, New
York, New York 10043 or at such other address as such party shall have furnished
to the Company in
                                       24

 
writing, (b) in the case of any other holder of Registrable Securities, at the
address that such holder shall have furnished to the Company in writing, or,
until any such other holder so furnishes to the Company an address, then to and
at the address of the last holder of such Registrable Securities who has
furnished an address to the Company or (c) in the case of the Company, at
McKesson Corporation, One Post Street, San Francisco, California 94104, to the
attention of its General Counsel, or at such other address, or to the attention
of such other officer, as the Company shall have furnished to each holder of
Registrable Securities at the time outstanding. Each such notice, request or
other communication shall be effective (i) if given by mail, 72 hours after such
communication is deposited in the mail with first class postage prepaid,
addressed as aforesaid or (ii) if given by any other means (including without
limitation, by air courier), when delivered at the address specified above,
provided that any such notice, request or communication to any holder of
Registrable Securities shall not be effective until received.

      9. Assignment. This Agreement shall be binding upon and inure to
         ----------
the benefit of and be enforceable by the parties hereto and their
respective successors and assigns. In addition, whether or not any express 
assignment has been made, the provisions of this Agreement which are for the 
benefit of purchasers or holders of Registrable Securities are also for the 
benefit of, and enforceable by, any subsequent holder of Registrable Securities.

     10. Descriptive Headings. The descriptive headings of the several
         --------------------
sections and paragraphs of this Agreement are inserted for reference only
and shall not limit or otherwise affect the meaning hereof.

      11. GOVERNING LAW. THIS AGREEMENT SHALL BE CONSTRUED AND ENFORCED
          -------------
IN ACCORDANCE WITH, AND THE RIGHTS OF THE PARTIES SHALL BE GOVERNED BY,
THE LAWS OF THE STATE OF DELAWARE WITHOUT REFERENCE TO THE PRINCIPLES OF
CONFLICTS OF LAWS.

      12. Counterparts. This Agreement may be executed simultaneously in
          ------------
any number of counterparts, each of which shall be deemed an original,
but all such counterparts shall together constitute one and the same
instrument.

      13. Entire Agreement. This Agreement embodies the entire agreement
          ----------------
and understanding between the Company and each other party hereto relating to
the subject matter hereof and supersedes and replaces all prior agreements and
understandings relating to the subject matter hereof.

      This Agreement shall become effective at the Effective Time. At the 
Effective Time, the Registration Rights Agreement, dated March 30, 1995, between
399 Venture and AmeriSource Distribution Corporation (now known as AmeriSource 
Health Corporation) and all other agreements and understandings with 399 
Venture, Citicorp Venture Capital Ltd. or any of their respective affiliates to 
register any securities of AmeriSource under the Securities Act or under any 
state securities law shall terminate without further action of the parties 
thereto.

      14. SUBMISSION TO JURISDICTION. ANY LEGAL ACTION OR PROCEEDING WITH
          --------------------------
RESPECT TO THIS AGREEMENT MAY BE BROUGHT IN THE COURTS OF THE STATE OF
DELAWARE OR OF THE UNITED STATES OF 

                                       25

 
AMERICA FOR THE STATE OF DELAWARE AND, BY EXECUTION AND DELIVERY OF THIS
AGREEMENT, THE COMPANY HEREBY ACCEPTS FOR ITSELF AND IN RESPECT OF ITS PROPERTY,
GENERALLY AND UNCONDITIONALLY, THE JURISDICTION OF THE AFORESAID COURTS AND
APPELLATE COURTS FROM ANY THEREOF. EACH PARTY HERETO HEREBY IRREVOCABLY CONSENTS
TO THE SERVICE OF PROCESS OUT OF ANY OF THE AFOREMENTIONED COURTS IN ANY ACTION
OR PROCEEDING BY THE MAILING OF COPIES THEREOF TO SUCH PARTY BY REGISTERED OR
CERTIFIED MAIL, POSTAGE PREPAID, RETURN RECEIPT REQUESTED, TO SUCH PARTY AT ITS
ADDRESS SPECIFIED IN SECTION 8. THE PARTIES HERETO HEREBY IRREVOCABLY WAIVE
TRIAL BY JURY AND ANY OBJECTION, INCLUDING, WITHOUT LIMITATION, ANY OBJECTION TO
THE LAYING OF VENUE OR BASED ON THE GROUNDS OF FORUM NON CONVENIENCE WHICH IT
MAY NOW OR HEREAFTER HAVE TO THE BRINGING OF ANY SUCH ACTION OR PROCEEDING IN
SUCH RESPECTIVE JURISDICTIONS.

      15. Severability. If any provision of this Agreement, or the
          ------------
application of such provisions to any Person or circumstance, shall be
held invalid, the remainder of this Agreement, or the application of such
provisions to Persons or circumstances other than those to which it is
held invalid, shall not be affected thereby.

                                       26

 
      IN WITNESS WHEREOF, the parties have caused this agreement to be duly 
executed as of the date first above written.

                                 MCKESSON CORPORATION

                                 By: /s/ Ivan D. Meyerson
                                    -------------------------------
                                         Ivan D. Meyerson


                                 399 VENTURE PARTNERS, INC.

                                 By:/s/ James A. Urry, V.P.
                                    -------------------------------
                                        James A. Urry, V.P.


                                       27